1. Field of the Invention
The present invention relates to a device for controlling the angle of an optical axis of a headlamp which can be used for a variable control of the angle of an optical axis of headlamps of, for example, automobiles and more particularly to an improvement in a control circuit for a headlamp optical axis control device.
2. Prior Art
Generally, in headlamp optical axis control devices of this type, two optical axis angle controllers (headlamp actuators) are installed in symmetrical positions on the left and right sides of a vehicle so that the controllers correspond to the respective headlamps installed on the left and right sides of the vehicle. Each of these optical axis angle controllers comprises: a motor which variably controls the angle of the optical axis of the headlamp on the basis of a control voltage set via an operation switch which includes a control voltage setting potentiometer; an optical axis angle voltage generating means including a potentiometer which generates a voltage corresponding to the angle of the optical axis of the headlamp that is controlled by the motor; and a comparative control means which makes a comparison between the optical axis angle voltage generated by the optical axis angle voltage generating means and the control voltage set by the operation switch and then causes the motor to rotate in a direction in which the difference between the two voltages obtained by the comparison approaches zero.
Compared to devices that use expensive electronic circuit components such as comparators, transistor arrays, motor drivers, etc., the conventional device as described above has advantages in that they can be built relatively inexpensively and in that they are compact and light-weight. However, they have problems. If one of the two optical axis angle controllers malfunctions, the optical axis can only be controlled by the remaining optical axis angle controller. This causes the circuit constants of the control circuit to be changed. The result is that an accurate optical axis angle control in response to the operation of the operation switch cannot be achieved, and the operation is performed with errors.